Cells constructed in this way are often alkali-manganese batteries, i.e., cells with a positive electrode of manganese dioxide (MnO2) and a negative electrode of zinc and an alkaline electrolyte, the latter being in particular based on potassium hydroxide (KOH). Generally, the positive electrode takes the form of a hollow cylinder, the outside surface of which contacts the inside surface of a cup-shaped cell housing. The negative electrode is arranged inside the positive electrode as is a separator for isolating the positive electrode physically from the negative electrode and at the same time allowing ion transport between the two electrodes.
The negative electrode is generally constructed by mixing the active zinc composition in the form of a zinc alloy powder with the alkaline electrolyte and a gelling agent. The mixture is distributed in the cavity formed inside the positive electrode or the cavity is filled with the mixture. A collector assembly is then inserted into the open end of the cup-shaped cell housing. The negative electrode is in this case preferably contacted via a pin-shaped collector which, on insertion of the collector assembly, is pressed into the cavity or into the negative electrode located therein. Finally, the cell housing is closed, generally by introducing a cover which is fitted over the collector assembly. To seal the cell, the walls of the cell housing may be crimped over this cover.
For manufacturing reasons in particular, the positive electrode in the form of a hollow cylinder is generally not introduced in one piece into the cup-shaped cell housing, but rather in the form of individual segments, which then form the positive electrode when assembled. For example, a disk-shaped segment may be inserted into a cylindrical, cup-shaped cell housing, on which a plurality of annular (ring-shaped) segments are then stacked. The inner diameter of the annular segments then determines the volume and diameter of the cavity for the negative electrode. The outer diameters of both the disk-shaped and annular segments are generally matched precisely to the corresponding inner diameter of the cup-shaped cell housing.
Electrochemical cells constructed as described certainly have a very high capacity. On the other hand, they also have the common feature of relatively high internal resistance which may lead to poor discharge characteristics. Those cells are not ideally designed for pulsed discharge profiles and for discharge under high current densities in particular, which means that they are not suitable or are suitable to only a limited degree for many applications.
It could therefore be helpful to improve the discharge characteristics of the above-mentioned generic electrochemical elements and expand their potential range of application.